Construction and Validation of a Novel "Pruritus Impact Scale" (PIS) for Assessment of Chronic Pruritus.

Abstract

Background: Currently available pruritus assessment tools may not always fulfill the needs of the Indian population and populations who share similar sociocultural backgrounds. To overcome this limitation, a new assessment tool "Pruritus Impact Scale (PIS)" was constructed and validated.

Aims and objectives: The primary objective is to construct and validate the novel PIS. The secondary objective is to evaluate the responsiveness of PIS to changes in symptoms.

Patients and methods: This study design was cross-sectional for the primary objective and longitudinal for the secondary objective. The study recruited 435 patients of chronic pruritus of different etiologies for the construction of the PIS scale. Patients were asked to fill out four different pruritus measuring tools i.e., Numerical Rating Scale (NRS), Dermatology Life Quality Index (DLQI), 12-item Pruritus Severity Score (PSS), and newly constructed PIS. The PIS was derived from existing standard assessment tools with certain modifications to keep a balance of psychometric properties of the scale and the sociocultural needs of the population. The validity and reliability of the scale was assessed. For detecting the response of PIS to change in pruritus intensity, 276 patients were followed and were instructed to refill all four scales at 6 weeks from the baseline. The responsiveness was judged by comparing the mean score of all scales at baseline with the mean score at 6 weeks. In addition, the changes in the scores among all 4 scales were correlated and compared.

Results: PIS showed strong internal consistency (Cronbach α = 0.882) and positively correlated with other validated pruritic tools such as NRS (ρ = 0.938, P < 0.0001), DLQI (ρ = 0.914, P < 0.01) and 12- PSS (ρ = 0.913, P < 0.001) at baseline. PIS showed satisfactory reproducibility at 3-hour intervals (Cronbach α = 0.994). Responsiveness to change in pruritus as measured by PIS at 6 weeks reassessment was correlated well with the changes in NRS (ρ = 0.689, P value < 0.0001), DLQI (ρ = 0.586, P value < 0.0001) and 12-PSS (ρ = 0.928, P value <0.0001).

Limitations: A noteworthy limitation of the present study is the lack of comparison of different items (within a construct) comprised in different tools used for comparison.

Conclusions: The newly constructed PIS is a valid tool in the studied population.